The invention relates to improvements in methods of and in apparatus for converting streams of particulate material into rods, especially to improvements in methods of and in apparatus for converting streams of fibrous material of the tobacco processing industry into continuous rod-like fillers. Still more particularly, the invention relates to improvements in a method of and in an apparatus for converting a surplus-containing stream of fibrous material into a rod by removing the surplus from the stream.
As used herein, the term "fibrous material" is intended to embrace natural, artificial and reconstituted tobacco as well as filter materials for the making of mouthpieces which are assembled with rod-shaped tobacco-containing articles to form filter cigarettes, cigars or cigarillos. The invention will be described mainly in connection with the making of plain cigarettes; however, the method and apparatus of the present invention can be utilized with equal or similar advantage for the making of rods which can be converted into other types of rod-shaped articles of the tobacco processing industry.
A cigarrette rod making machine employs a distributor which delivers fragmentized particles of tobacco leaves, fragmentized sheets of reconstituted tobacco and/or fragments of artificial tobacco to a stream building zone wherein the particles form a continuous stream. Such stream contains a surplus of fibrous material and is converted into a continuous rod during travel with a conveyor past a trimming or equalizing device which removes the surplus. The resulting rod (also called filler) is thereupon condensed and draped into a web of cigarette paper or other suitable wrapping material to form with the weeb a cigarette rod which is subdivided (e.g., by a conventional cutoff) into sections of unit length or multiple unit length. The thus obtained cigarettes are delivered to storage, to a packing machine or to a filter tipping machine. Certain types of filter rod sections are or can be produced in a similar manner except that the fibrous material which forms the stream is a substance which intercepts certain presumably harmful ingredients of tobacco smoke when it constitutes the rod-shaped component of the filter mouthpiece in a filter cigarette.
It is further known to monitor one or more characteristics of the stream and/or rod during the making of cigarettes. To this end, the stream or the rod is caused to pass along one or more monitoring devices which are designed to ascertain the density of successive increments of conveyed fibrous material, the mass of fibrous material in successive increments of the stream or rod, or the height of successive increments of the stream or rod.
In certain recent types of cigarette making machines, the distributor (also called hopper) is designed to draw fibrous material from a magazine, to convert the withdrawn material into a thin running layer or carpet, and to feed successive increments of the leader of the carpet into a pneumatic conveyor which delivers fibrous material to a suction conveyor in the stream building zone. The suction conveyor normally constitutes an endless foraminous belt conveyor one side of which is adjacent a suction chamber so that the fibrous material leaving the pneumatic conveyor is attracted to the other side of the foraminous conveyor where it grown into a continuous stream which contains a surplus of fibrous material. The term "surplus" or "excess" denotes that additional quantity of fibrous material which must be removed from the stream in order to transform the latter into a rod which is ready to be converted into the filler of a cigarette rod offering a requisite resistance to compression. The trimming or equalizing device removes the surplus from successive increments of the moving stream, and such surplus is normally returned to the distributor wherein it is mixed with fresh fibrous material prior to being returned to the stream building zone.
In order to ensure the making of a satisfactory rod, it is desirable to form the stream with a high percentage of surplus so as to guarantee that eventual unevennesses of the stream will not influence the quality of the ultimate products, i.e., that the trimming device will be required to remove at least some surplus from each and every increment of the stream. On the other hand, it is also desirable to form the stream with a minimum of surplus because the removed surplus includes, at least in part, relatively short (less desirable) tobacco shreds and the particles which form the surplus are likely to undergo additional comminution and/or to change their moisture content during transport from the trimming station back to the distributor. In other words, it is desirable to form the stream with a surplus which contains sufficient quantities of fibrous material to ensure the making of a high-quality product but is not excessive so that it will not entail unnecessary comminution, drying and/or other undesirable changes of characteristics of fibrous material which must be returned to the distributor for renewed delivery into the stream building zone.
As a rule, a stream of tobacco shreds or similar fibrous material will be formed on the foraminous belt conveyor between two lateral walls so that three of four sides of the stream are shaped by the adjacent surfaces of the conveyor and of the lateral walls. However, the fourth side (opposite the conveyor) normally exhibits more or less pronounced hills and valleys which are unavoidable (at least by resorting to heretofore known distributors) when the material of the stream consists of more or less interlaced shreds including longer and shorter shreds in an infinite number of different orientations. The parameters which influence the development and the pronouncedness of hills and valleys at one side of the fully grown stream which advances toward the trimming station in a cigarette rod making machine include the ratio of short and long shreds in the stream, the blend (i.e., the ratio of two or more types of tobacco in the stream), the temperature of fibrous material, the moisture content of fibrous material, the quality of the distributor and certain others.
Certain presently known proposals to influence the making of a continuous stream of fibrous material in such a way that the stream will contain adequate quantities of surplus but that the surplus will not be excessive are disclosed in commonly owned U.S. Pat. No. 3,132,650 to Richter, in U.S. Pat. No. 3,338,247, in commonly owned U.S. Pat. No. 4,063,563 to Lorenzen, in commonly owned U.S. Pat. No. 4,190,061 to Heitmann, in commonly owned U.S. Pat. No. 4,556,071 to Hoffmann and in British Pat. No. 2,134,367.